1. Field of the Invention
The present invention relates to, for example, an image forming apparatus comprising an image reading device that obtains image data from a copy target.
2. Description of the Related Art
An image forming apparatus comprises a photosensitive member on which an electrostatic image and a developer image are formed and a charging device that charges the photosensitive member to a predetermined potential.
Known charging devices use a wire-, brush-, or needle-like electrode.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2000-242060 (Abstract, claim 1, FIG. 1, paragraphs [0024], [0025], and others) discloses a technique employing a charging device having a wire-like electrode. With this technique, a piezoelectric transformer is connected to the wire-like electrode so as to supply a high-voltage to the wire-like electrode. Then, the wire is prevented from being contaminated by transmitting to the wire a mechanical vibration which generated when the piezoelectric transformer is driven.
Further, Jpn. Pat. Appln. KOKAI Publication No. 2002-123068 (Abstract, claim 1, FIG. 1, paragraphs [0006], [0007], and others) discloses a technique employing a charging device having a brush-roller-like electrode. With this technique, vibration is generated in an axial direction to cause attachments adhering to an outer peripheral surface of the brush roller to float. Then, sucking means is used to collect the attachments.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. 5-107867 (Abstract, claim 1, FIG. 1, paragraphs [0024], [0025], and others) discloses a technique also employing a charging device having a brush-roller-like electrode. With this technique, vibration is generated in the axial direction to prevent non-contact between the brush roller and a photosensitive drum in the axial direction. The photosensitive drum is thus charged to a uniform potential.
Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 2000-58224 (Abstract, claim 1, FIG. 3, and others) discloses a technique employing a charging device having a saw-tooth-like electrode. With this technique, a cleaning member is abutted against the saw-tooth-like electrode. The cleaning member then moves parallel to the electrode to remove contamination from the electrode.
As described above, when attachments adhere to a charging device charging a photosensitive member, disadvantageously the entire photosensitive member is not uniformly charged. In particular, if a needle-like electrode such as the one shown in Patent Document 4 is used, when a developer or attachment such as dust which floats through a main body adheres to the needle-like electrode, an insufficient discharge may occur in the adhering parts. Thus, a nonuniform discharge may occur on the surface of the photosensitive member; that is, a nonuniform potential may be formed in the axial direction. This may prevent a satisfactory image from being formed.
Further, with the technique disclosed in Patent Document 4, the cleaning member is brought into contact with the needle of the electrode. Consequently, the needle may be bent by the cleaning member caught at the tip of the needle. On this occasion, the bent needle cannot cause a sufficient discharge, resulting in a nonuniform discharge from the surface of the photosensitive member. This may prevent a satisfactory image from being formed.